A known driving unit is employed for opening or closing a back door of a vehicle. Such driving unit is disclosed in Japanese Patent Laid-Open Publication No. 2000-96913. According to the disclosed driving unit, an end portion of a back door is pivotally supported on a vehicle body via a supporting shaft. The back door can be then open or closed by means of the driving unit including an electric motor. This type of back door can be open or closed manually as required. The driving unit includes a driving pin rotatable in reciprocating manner by means of the electric motor and operates the back door in opening or closing direction thereof by contacting the driving pin with a driving arm connected to the back door. According to the aforementioned structure, the driving pin returns to a predetermined position whenever the opening or closing operation of the back door is completed so that the back door can be open or closed manually. Thus, the driving arm is rotatable without being restrained by the driving pin. The back door having the aforementioned structure is maintained at a fully open position thereof by means of a gas stay.
According to the disclosed driving unit, the driving pin is in contact with the driving arm so as to open or close the back door. Therefore, for example, the back door is closed by the operation of the driving unit within a range specified with a solid line shown in FIG. 9A during the closing operation. However, the back door is closed by the operation of the gas stay within a range specified with a dashed line in FIG. 9A. Even if an obstacle such as A in FIG. 9A is pinched between the back door and the vehicle body, the back door cannot be stopped by the operation of the driving unit. In the same way, the back door cannot be stopped within the range specified with the dashed line in FIG. 9B during the opening operation.
Thus, a need exists for a driving unit that can stop or reverse the back door by means of the operation of the driving unit during the opening or closing operation of the back door.